Wrought nickel bronze



United States PatentO 2,768,102 ,WROUGHT NICKEL BRONZE Carl M. Zvanut,Midland, Mich., assignor to Olin Mathieson Chemical Corporation, acorporation of Yirginia NoDrawing. Application January 31,1952,

Serial N0..269,331 1 10 Claims. (Cl. 1482) J This invention relates to amethod of l processing of copper alloys and pertains more specificallyto the making of a novel tough, wear and corrosion resistant alloy ofthe nickel bronze type in the wrought form in contradistinction to thecast form. Generally, the term nickel bronze includes age-hardenablealloys containing from about 3 /2% to 50% nickel, from about 3% to 20%tin, not more than about 10% zinc, if any, and the balance copper. Acommercially well-known composition of this type consists of about 88%copper, 5% nickel, 5% tin, and 2% zinc and is referred to by theindustry as 88552 nickel bronze.

Heretofore, the most commercially desirable copper base alloyscontaining tin,- nickel and frequently some zinc in addition to copper,have been generally employed in theform of castings largely becausethese alloys are not readily worked while cold and also lack the hotductility necessary for hot rolling. It has been customary to cast thesealloys by meltingthem in a suitable furnace having a clay-graphitecrucible, for example, undera cover of carbon, generally charcoal, .orno applied cover at all, and after a suitable oxidizing treatment withcuprous oxide and a final deoxidizing treatment with phosphorus, themolten metal. is poured into a mold having a carbonaceous dressing,including either graphite or lampblack. Although it has been known thatsuch bronzes, after casting in the form of an ingot, could be fabricated2,768,102 Patented Oct. 23, 1956 It is, therefore, an object of thisinvention to provide a commercially feasible method. of producingwrought nickel bronze of the type described. Another object is thesimplification of the manufacture of nickel bronze sheet metal andparticularly elimination of the long and costly annealing treatment forthe cast metal heretofore considered necessary prior to reduction byrolling. Another object is the provision of a novel alloy of the nickelbronze type amenable to rolling. Still another object is to provide anew and improved method of making wrought articles of such bronzes.Other objects will be apparent from the accompanyingdescription.

This invention is predicated on the discovery that an age-hardenablenickel bronze may be directly worked as cast to form a wrought article,such as rolled strip,of excellent quality provided the cast metal isproduced substantially free from carbon phosphorus, and slag inclusionsand provided the metal is treated with manganese. To avoid carbon, nocharcoal, graphite, lampblack or the like is employed in the walls ofthe molten metal bath holding crucible, or in the molten metal bathcover as a deoxidizing agent, or in the dressing for the mold into whichthe metal is cast to, form the desired ingot. The molten metal is castinto a mold coated with a non-volatile carbon free dressing, preferablybone-ash, to avoid intro-' duction of any carbon into the metal duringpouring from the crucible into the mold. Phosphorus, heretofore regarded by the art as a suitable deoxidizer for many copper base alloysincluding nickel bronze, is not suitable for the purposes of thisinvention because phosphorus, when present, even in small amounts, wasfound to-accentuate the age-hardening properties of the bronze in such away as to render the metal unfit for cold rolling by the usual methods.Manganese, which also accentuates the agehardenability of these bronzes,which in itself is not undesirable, was found toresult in no impairmentof the workas a wrought product, such as sheet, working of the cast ing.While the quenchedmetalcan be worked well initially, upon subsequentcold rolling after the usual anneal at around 750 C. the surface of thestrip in rolling develops severe fire cracks renderingv the metalutterly useless for further fabrication to desiredgauge and temper. Onthe other hand, the specially treated metal which is slowly cooled,unlike the quenched metal, is rather brittle and on breakdown rollingdevelops edge cracks necessitating removal of a considerable portion ofmetal including these cracks before further finishing operations can beconducted on the metal. Furthermore, this type of bronze exhibits whilemolten a tendency to take up inclusions of anon-metallic character,believed to be slag, which may be so widely distributed within the solidmetal of the casting as to render it unfit for further processingpreparatory to ultimate use of the metal in manufacture of articlesrequiring asurface free of blemishes. Because of i ability of bronzedeoxidized with the manganese. .In deoxidizing the molten metal,therefore, manganese is employed and preferably is included as a residuein theresulting nickel bronze to the extent of not more than. about0.2%. To protect the metal during the melting operation from excessivecontact with the atmosphere and to control any slag formed, a' cover isemployed on the molten metal bath such that slag will be entrained inthe cover and such as is sufiiciently viscous or coherent that the coveritself is not a source of undesirable inclusions in the cast metal. Acover which produces favorable results consists largely of particles ofa refractory material, i. e., of sand, the fluidity of which is modifiedby the inclusion of more easily fused materials such as common salt,borax, a glass or the like. A preferred composition consists of about ormore sand and the balance salt. In accordance with this invention,wrought nickel bronze is made by a process involving melting the metalunder a cover which prevents carry-over of slag into the casting duringpouring, deoxidizing the metal with manganese, pouring the molten metalthus prepared into a mold coated with a non-volatile carbon freedressing and thereafter directly working the solidified ingot by coldrolling.

A readily worked nickel bronze alloy produced in accordance with thisinvention comprises copper, nickel, tin, usually zinc, and a residualamount of manganese, and is further characterized by freedom from carbonand phosphorus and by a high density in the as cast condition. Aresidual manganese content of the order of about 0.2% or less andpreferably not in excess of about 0.05% is contemplated. The as castdensity of an 88- 5-5-2 type of nickel bronze made as described hereinis better than 8.72 gram per cubic centimeter and is high relative to'the density of the rolled metal which is 8.93 grams per centimeter. Forthe 88-552 type alloy,

which is about the only commercially important nickel bronze, an as castdensity of about 8.75 grams per centimeter or better is consistently oneof the characteristics of metal which may be directly cold rolled tostrip with intermediate annealing at a temperature of about 650 C.

In carrying out a preferred embodiment of this invention, constituentmetals of suitable purity, beginning with copper and nickel, are chargedinto any suitable melting apparatus, such as the low frequency electricinduction furnace of the type shown in U. S. Patent No. 1,201,671,having a molten metal bath holding crucible, the walls of which consistof a refractory ceramic material of the sillimanite type or the like,but in no instance of claygraphite, or any other carbonaceous mixture.In order to prevent oxidation of the molten metal and inhibit theformation of slag in the crucible, a cover is provided over the melt andconsists of about 80% or more sand and the balance common salt or thelike in amounts suflicient to adjust the fluidity of the cover asdesired. This protective cover is capable of entraining any slag formedand has a viscosity and coherency such that on casting of the metal nopart of the cover will carry over so as to form slag inclusions in thecasting. Since the melting and pouring of nickel bronze is done at atemperature of around 1250 C. or 1300 C., relatively high for copperbase alloys, many cover materials such as common salt and borax, likethe naturally occurring slag, prove entirely too fluid at this elevatedtemperature, and, if used, allow formation of inclusions folded into thesurface and even into the body of the casting which must then be eithersubject to intensive milling to remove surface defects before it can berolled or must be entirely scrapped as where the inclusions aredistributed throughout the body of the casting. At all times during themelting operation the surface of the molten metal is maintained underthe cover since it has been found that skimming the surface, as iscustomary with many alloys, is detrimental and reflected by theinclusion of slag in the casting. About 30 minutes before the melt hasreached the emperature for pouring, electrolytic manganese is added inamounts sufficient to deoxidize the molten metal, leaving a residue ofabout 0.05 manganese. For strip rolling the molten metal is poured at atemperature around 1250 C. and preferably around 1300 C. into a suitablemold such as a vertical water-cooled metal mold having a casting cavitymeasuring 15 /2 X 2 /2" x 96", for example, coated with a dressing ofbone-ash.

On solidification 88-5-52 type of nickel bronze cas ingots made asdescribed are found to contain substantially only manganese in residualamounts in addition to the chief constituent metals of nickel bronze;and the ingots are further characterized by high density. Typicalanalyses and densities of ingots produced are shown in the table whichfollows. The low density figure for each ingot is obtained on a testsample selected at a central portion of the casting; and the highdensity figure for each ingot is obtained on a test sample selected atand including one or more lateral original surface areas of the castingincluding the most dense portion of metal. The center sample is boundedby cut surfaces and includes none of the original lateral surfaces ofthe casting.

The nickel bronze ingots produced have an average density at least ashigh as about 8.75 grams per cubic 30 minutes to one hour.

centimeter and are characterized by physical properties such as aductility suflicient to render the metal amenable to fabrication towrought metal and particularly to rolled strip of any desired gauge by acold rolling and intervening annealing technique to which thenon-ferrous rolling mill is adapted. The difiicultly workable 88-5-5-2nickel bronze made by the heretofore common prior art method is as arule characterized by average densities low in comparison'to that of theingots produced.

Test samples of the cast metal are capable of withstanding a 180 bend ona. /2" radius without fracture indicating that the casting produced issufficiently ductile to be amenable to cold working by rolling and thelike. The dense slag-free cast metal of this invention can be coldrolled without a special preliminary homogenizing heat treatment andbetween cold rolling reductions the metal may be annealed inconventional apparatus at a temperature of about 650 C., for a periodfrom about Reduction by rolling proceeds without development of edge orsurface cracks; and the metal surface may be finished to a high lustrefree of blemishes such as would be formed by slag inclusions.

The rolled and otherwise wrought nickel bronze may be age-hardened afterfabrication to obtain optimum properties such as high strengthattainable with these bronzes. In addition to the constituents specifiedthe metal may contain other elements in such amounts as do not impairthe desired properties and nature of the alloy produced.

It is to be understood that deviations may be made from the embodimentof the invention described herein without departing from the spirit andscope thereof as defined in the appended claims.

The invention claimed is:

1. In the art of making nickel bronze consisting essentially of 88%copper, 5% nickel, 5% tin and 2% zinc amenable to cold rolling directlyfrom the as cast condition the process which comprises forming a meltsubstantially free from phosphorus and carbon, maintaining over saidmelt a protective cover of at least about sand and the balance salt,deoxidizing said melt by the addition of electrolytic manganese to leavea residue of about 0.05% manganese in said bronze, and pouring themolten metal of said melt into a vertical water-cooled mold coated witha bone-ash dressing, thereby forming an ingot having an as cast averagedensity of at least about 8.75 grams per cubic centimeter andsubstantially completely free from phosphorus, carbon and slaginclusions.

2. The process of making wrought nickel bronze consisting of about 88%copper, about 5% nickel, about 5% tin and about 2% zinc, comprisingforming in a crucible a melt of the constituent metals, maintaining aprotective cover of at least about 80% sand and the balance salt overthe molten metal of said crucible, deoxidizing the melt by addition ofmanganese to leave a residue not in excess of about 0.2%, pouring themolten metal from said crucible into a vertical water-cooled mold coatedwith a bone-ash dressing to form a dense ingot substantially completelyfree from carbon, phosphorus and slag inclusions and subsequentlysubjecting said ingot to a series of cold working and intermediateannealing steps to reduce the ingot to a desired article shape.

3. The process of making rolled nickel bronze which comprises forming ina crucible a melt consisting essentially of about 88% copper, about 5%nickel, about 5% tin and about 2% zinc, maintaining a protective coverpredominantly of sand free from carbonaceous material over the moltenmetal in said crucible, deoxidizing the melt by addition of manganese toleave a residue not in excess of 0.2%, pouring the molten metal fromsaid crucible into a vertical water-cooled mold coated with a bone-ashdressing, thereby forming an ingot having an as cast density of at leastabout 8.72 grams per cubic centimeter and substantially completely freefrom carbon, phosphorus and slag inclusions, and subsequently subjectingsaid ingot to a series of cold working and intermediate annealing stepsto reduce the ingot to a desired gauge.

4. The process of making wrought nickel bronze which comprises formingin a crucible a melt consisting essentially of copper, nickel, tin andzinc, maintaining over the molten metal in said crucible, a protectivecover predominantly of sand free from carbonaceous material modifiedwith a fused salt, deoxidizing the melt by addition of manganese toleave not more than a residue of manganese, pouring the molten metalfrom said crucible into a vertical water-cooled mold coated with aboneash dressing to form an ingot substantially completely free fromphosphorus, carbon and slag inclusions, and working said ingot as castto deform the ingot to a desired article shape.

5. The process of making wrought nickel bronze consisting of about 88%copper, about nickel, about 5% tin and about 2% zinc, forming a melt ofsaid constituent elements, maintaining a protective cover of at least80% sand and the balance salt over the molten metal, deoxidizing themelt by addition of manganese to leave a residue not in excess of 0.2%in said bronze, pouring the molten metal from said crucible into avertical water-cooled mold coated with a bone-ash dressing, therebyforming an ingot having an as cast density of at least 8.75 grams percubic centimeter and substantially completely free from phosphorus,carbon and slag inclusions, and subsequently subjecting said ingot to aseries of cold Working and intermediate annealing steps to reduce theingot to a desired gauge and temper.

6. The process of producing Wrought nickel bronze consisting essentiallyof about 3 /z% to 50% nickel, about 3% to 20% tin, less than about 10%zinc, with the balance copper, which comprises forming a melt of saidconstituent elements, maintaining a protective cover predominantly ofsand free from carbonaceous material over said melt, introducingelectrolytic manganese in amounts sufficient to deoxidize said melt toleave a residue not in excess of about 0.2%, chill casting the moltenmetal into a water-cooled mold coated with a non-volatile carbon-freedressing to form a dense ingot, substantially completely free fromcarbon, phosphorus and inclusions of slag, and subsequently subjectingsaid ingot to a series of cold-working and intermediate annealing stepsto reduce the ingot to a desired article shape.

7. The process of making wrought nickel bronze which comprises formingin a crucible a melt consisting essential of copper, nickel, tin andzinc, maintaining a protective cover predominantly of sand substantiallyfree from carbonaceous material over the molten metal in said crucible,deoxidizing the melt by addition of manganese to leave a residue ofmanganese not in excess of about 0.05% in said bronze, pouring themolten metal from said crucible into a vertical water-cooled mold coatedwith a bone-ash dressing, thereby forming an ingot composed of about 88%copper, about 5% nickel, about 5% tin and about 2% zinc, having an ascast density of at least 8.72 grams per cubic centimeter and free fromphosphorus, carbon and slag inclusions, and subsequently subjecting saidingot to a series of cold working and intermediate annealing steps toreduce the ingot to a desired article shape.

8. In the art of making nickel bronze amenable to cold working directlyfrom the as-cast condition the process which comprises forming a meltconsisting essentially of copper, nickel, and tin maintaining over themelt a protective cover of sand at least about and the balance a saltmore readily fused than sand, said cover being substantially free fromcarbonaceous material, deoxidizing said melt with manganese to leave aresidual amount of manganese, if any, not in excess of about 0.05%, andchill casting the molten metal in a mold coated with a non-volatilecarbon-free dressing to produce a dense ingot substantially completelyfree from phosphorus, carbon and slag inclusions.

9. In the art of making nickel bronze amenable to cold working directlyfrom the as-cast condition the process which comprises forming a meltconsisting essentially of copper, nickel, and tin, maintaining over themelt a protective cover predominantly of sand substantially free fromcarbonaceous material and modified by the inclusion of a more readilyfused material, deoxidizing said melt with manganese to leave a residueof manganese not substantially in excess of about 0.2% in the castmetal, and chill casting the molten metal into a mold coated with anon-volatile, carbon-free dressing to produce a dense ingotsubstantially completely free from phosphorus, carbon and slaginclusions.

10. The process of making wrought nickel bronze which comprises formingin a crucible a melt consisting essentially of copper, nickel, tin andzinc, maintaining over the molten metal in said crucible, a protectivecover predominantly of sand free from carbonaceous material modifiedwith a fused salt, deoxidizing the melt by addition of manganese toleave a residue of manganese not substantially in excess of about 0.2%,pouring the molten metal from said crucible into a vertical water-cooledmold coated with a bone-ash dressing to form a dense ingot substantiallyfree from phosphorus, carbon and slag inclusions, and cold working saidingot as cast to deform the ingot to a desired article shape.

References Cited in the file of this patent UNITED STATES PATENTS598,632 Johnston Feb. 8, 1898 1,586,871 White June 1, 1926 1,851,218Stone Mar. 29, 1932 1,906,567 Fritschle May 2, 1933 1,928,747 Wise Oct.3, 1933 2,116,207 Lindner et .al. May 3, 1938 2,266,734 Behrendt Dec.23, 1941 2,372,202 Hensel et al. Mar. 27, 1945 2,401,818 Eckel June 11,1946 2,445,868 Berwick July 27, 1948 2,577,426 McCullough Dec. 4, 1951OTHER REFERENCES Melting and Casting of German Silver Alloys, by EdmundR. Thews, Fiat Final Report No. 878, Oifice of Military Government forGermany (U. 8.), Field Information Agency Technical, July 23, 1946,pages 9 and 10.

1. IN THE ART OF MAKING NICKEL BRONZE CONSISTING ESSENTIALLY OF 88%COPER, 5% NICKEL, 5% TIN AND 2% ZINC AMENABLE TO COLD ROLLING DIRECTLYFROM THE AS CAST CONDITION THE PROCESS WHICH COMPRISES FORMING A MELTSUBSTANTIALLY FREE FROM PHOSPHORUS AND CARBON, MAINTAINING OVER SAIDMELT A PROTECTIVE COVER OF AT LEAST ABOUT 80% SAND AND THE BALANCE SALT,DEOXIDIZING SAID MELT BY THE ADDITION OF ELECTROLYTIC MANGANESE TO LEAVEA RESIDUE OF ABOUT 0.05% MAGANESE IN SAID BRONZE, AND POURING THE MOLTENMETAL OF SAID MELT INTO A VERTICAL WATER-COOLED MOLD COATED WITH ABONE-ASH DRESSING, THEREBY FORMING AN INGOT HAVING AN AS CAST AVERAGEDENSITY OF AT LEAST ABOUT 8.75 GRAMS PER CUBIC CENTIMETER ANDSUBSTANTIALLY COMLETELY FREE FROM PHOSPHORUS, CARBON AND SLAGINCLUSIONS.